1. Field of the Invention
The present invention relates to a torque transmitting device for a vehicle and more particularly to a torque transmitting fan drive assembly having a thermostatic ring connected to a valve member for controlling the position of the valve member to vary the volume of torque transmitting fluid in an operating chamber in the coupling in response to the ambient temperature of the torque transmitting device, and wherein a bolt member extends coaxial to the axis of rotation for supporting the torque transmitting device on a shaft of an engine associated with the vehicle. Additionally, a counterbalancing means is provided responsive to centrifugal force acting thereon upon rotation thereof to counterbalance the centrifugal forces acting on the thermostatic ring upon rotation of the thermostatic ring.
2. Background of the Invention
There are many known torque transmitting fan drives in the prior art. Some of these fan drives, such as illustrated in the Sutaruk U.S. Pat. No. 3,512,622, disclose the use of a through bolt coaxially disposed for supporting the torque transmitting mechanism on an engine shaft. However, the bimetal valve of Sutaruk in the through bolt design is responsive to the internal temperature of the fan drive and not the temperature of the ambient air around the fan drive. Preferably, the fan drive acts to blow cooling air over the radiator of a vehicle. The air passing over the radiator and through the fan drive has an ambient temperature which is indicative of the temperature of the water in the radiator. Thus, sensing ambient air temperature allows the fan drive to be controlled in a direct relationship to the temperature of the fluid in the radiator of the vehicle. The Sutaruk design which discloses a bimetal element interiorally of the fan drive would not be responsive to the ambient air temperature but rather to the temperature of the fan drive itself which changes very slowly due to its mass. Thus, the internal temperature of the fan drive will not be directly related to the temperature of water in the radiator of the vehicle.
Another prior art fan drive disclosed in Sutaruk utilizes a thermostatic coil which senses the ambient air temperature. However, the use of the known thermostatic coil which senses ambient air temperatures prevents the use of the through bolt disposed coaxial to the axis of rotation for mounting the fan drive due to the fact that the coil is centrally mounted on the axis of rotation of the unit. In some instances, it is desirable to utilize a through bolt for mounting the fan drive unit having a temperature responsive element which is responsive to the ambient temperature of the torque transmitting device rather than the internal temperature of the torque transmitting device.
In order to solve the problem of providing a through bolt design which is responsive to the ambient temperature of air surrounding the torque transmitting unit, it has been decided to utilize a thermostatic ring which is mounted to the cover of the unit and which is disposed with its center coaxial to the axis of rotation of the unit. A through bolt can then be inserted through the central opening in the thermostatic ring and through the coupling members to secure the unit to a shaft of a vehicle engine. The use of a thermostatic ring rather than a thermostatic coil causes problems due to the centrifugal force which acts on the ring when the ring and fan drive rotate. In order to overcome this problem, a counterbalancing means has been provided to counterbalance the centrifugal force which acts on the thermostatic ring.